The present invention relates to improving the green strength of various synthetic elastomers. More specifically, the present invention relates to obtaining improved green strength of various elastomers by forming a copolymer therewith through the use of specific hydroxyl containing monomers. The green strength can be further improved by utilizing specific cross-linking agents to cross-link the copolymers. Additionally and preferably, the present invention relates to the addition of the above-noted hydroxyl containing copolymers to various synthetic elastomers or natural rubber to form blends which selectively are cross-linked with hydroxyl ester cross-linking agents wherein such blends have improved green strength.
Heretofore, although progress in the elastomer field has improved to such an extent that synthetic elastomers have supplemented or replaced natural rubber to a large extent in the fabrication of tires or other rubber products, synthetic elastomers still generally exhibit low green strength. This is true even for synthetic cis-1,4-polyisoprene. By the term "green strength" it is generally meant that property of a polymer or elastomer common in natural rubber, which contributes to the proper building conditions where multiple components are employed and which result in little or undesirable relative movement of the assembled components subsequent to assembly and prior to initiation of the curing operation. Generally, green strength is measured by stress-strain measurements.
Among the various compounds or agents which have been utilized to improve green strength of synthetic rubber elastomers is maleic acid as set forth in U.S. Pat. No. 3,893,983, maleic anhydride with a free radical initiator as set forth in U.S. Pat. No. 3,897,403 and maleinized polyisoprene rubber composition containing a compound of the metal of groups 2 and 4 of the Periodic Table as set forth in U.S. Pat. No. 3,898,193. However, these patents do not relate to the formation of copolymers with hydroxyl containing monomers and the like.